Electro-magnetic and structural analysis of six-pole hybrid-excited permanent magnet motors

Potentials and limits of the Hybrid-Excitation Permanent-Magnet (HEPM) synchronous machine are dealt with in this paper. A six-pole machine is taken into consideration, and both parallel and series configurations are analysed and compared. Taking advantage of the rotor excitation coils, the permanent magnet (PM) rotor flux can be adjusted according to the operating speed to improve its performance parameters. The electro-magnetic force is analysed in its first harmonic and in the complete shape. Moreover, a comparison between analytical and numerical formulation has been done for the rotor current control. In particular, the speed range is extended, and electro-mechanical torque and power are increased, as well as the efficiency. It will be shown that the rotor flux reduction by using the excitation winding yields an improvement of the motor performance. The main advantage will be obtained during the flux-weakening operations. In this paper, different rotor topologies will be analysed to highlight the advantages and drawbacks of each of them, and how it is possible to achieve higher speed with higher torque and without high saliency ratio. A magnetic network will be introduced to explain the different contribution of the excitation winding to the rotor flux. Furthermore, a comparison of the amount of the volume of PM, copper and iron in internal permanent magnet (IPM) motor and HEPM motor will be analysed. Actually, an analysis of the harmonic content in the electro-motive force even varying the excitation current and a mechanical stress analysis of each machine will be shown. Finally, it will be verified that the excitation losses represent a minimum component of the total losses.